In industrial installations for handling, processing, or filling a series of containers such as bottles, cans, etc., at a high rate, it is sometimes essential during transfer of the containers to inject a predetermined dose of liquid into each container. The dose is often of small volume (conventionally lying in the range 0.1 ml to 10 cl), and the liquid is sterile since it is intended for human or animal consumption or for making up pharmaceuticals or toiletries.
Since the containers are processed in large numbers at a very high rate, the problem arises of being able to provide an automatic metering-out apparatus capable of delivering very small volume doses of liquid at a very high rate, with great accuracy, and with great reliability.
Known metering-out apparatuses are either entirely manual, i.e. driven by a person, in which case they do not have the required reliability and accuracy, or else they include electromechanical, electronic, or even computer devices that are extremely complex and expensive and that are difficult to adjust in operation. In addition, known electronic or computer devices are not very compatible with installations for handling, processing, or filling bottles since such installations are essentially mechanical and thus may perform operations that are inaccurate or random. Similarly, devices that are electrically driven are not very compatible with the liquid in the environment of such installations for handling, processing, or filling containers.
Various types of liquid-metering pumps are known which suck up a predetermined quantity of liquid from a duct and then deliver it into another duct. Nevertheless, such pumps are not entirely compatible with operation at a high rate for the purpose of metering out very small quantities, and they are not sufficiently accurate and reliable. For example, mere wear of sealing rings can give rise to an unacceptable change in the volume pumped and metered out.